To get the Launcher to work in Linux, I had to:

1) Edit FFXIV_BOOT.CFG and change value of line WebView2RuntimeInvalid from 0 to 1.
2) Use Protontricks/Winetricks to uninstall WebView2.

The CFG file is in your Proton/Wine prefix for the game. Folder where you can find it is:

Code:
<prefix>/drive_c/users/steamuser/Documents/My Games/FINAL FANTASY XIV - A Realm Reborn/
(My use case is Arch Linux with Steam version of the game.)